Abstract:

Large eddy simulation (LES) in an axisymmetric piston-cylinder geometry was carried out using three LES approaches: 1) Smagorinsky subgrid scale model, 2) implicit LES, and 3) scale selective discretisation (SSD). In addition to the LES subgrid scale model sensitivity study, two additional simulations were carried out in order to understand the roles of the intake and the in-cylinder residual turbulence to the flow statistics. Altogether twelve cycles were computed for each simulation on a grid with 5 million cells and requiring over a month of wall-clock time per simulation on a supercomputer. Analysis of velocity statistics revealed that the results were not very sensitive to the LES model type. However, the residual turbulence was noted to have a clear impact on the velocity statistics. In particular, the simulations revealed that removing the residual turbulence from the intake region at the top-dead-centre has a clear impact on the overall velocity statistics. In many cases the cycle-to-cycle variation (CCV) increased. In a respective numerical test, where only the in-cylinder turbulence was removed at top-dead-centre, weaker sensitivity was observed. In addition, the CCV relative to the mean velocity was in some cases as high as 30 \% even in such a non-reactive case. The present study complements previous studies on the same set-up by investigating the sensitivity of three LES models on flow statistics, quantifying CCV using three different LES approaches in the standard set-up, and assessing the role of residual turbulence on the flow statistics via modified flow cases.